1. Field of the Invention
The present invention relates to a projection lens apparatus for allowing a source light to be made incident in an image display apparatus so that an overhead projection of the reflected light or the transmitted light is performed on a projection screen, and also relates to a projection type image display apparatus equipped with the projection lens apparatus.
2. Description of the Prior Art
The main stream of a projection type image display apparatus has been a type that performs an overhead projection of an image formed in a CRT. In order to improve the efficiency of light usage, and reduce the size and the weight of the apparatus, a projection type image display equipped with a liquid crystal display element and a micro mirror display element (hereinafter, referred to as a DMD element) instead of a CRT has been recently developed. This projection type image display apparatus is configured such that a source light is modulated by transmitting or reflecting it at each pixel in accordance with video signals applied to the above display element, thereby allowing a projection lens apparatus to perform a overhead projection and thus form an image.
Although the image display apparatus equipped with a CRT is capable of electrically compensating distortion aberration of a projection image, the image display apparatus equipped with a liquid crystal display element or a DMD element is not. For that reason, the latter apparatus is required to optically compensate the distortion aberration.
A projection type lens apparatus using liquid display elements also has been developed as set forth, e.g., in JP-A-11-149041 specification, however, it has a drawback of a short back focus of about 20 mm.